1. Field of the Invention
The present invention relates to a hitch assembly for semi-trailers mounted on a platform such as a railroad flat car. More particularly the invention relates to a hitch assembly adapted for positively securing the forward end portion of a semi-trailer for travel on a moving flat car piggyback fashion with the depending kingpin of the trailer in detachable locking engagement with the hitch assembly. The hitch assembly is mounted on a carriage mechanism adapted to elevate a support bed into an operative position at the proper level above the platform of the flat car for engagement with a semi-trailer. The carriage mechanism is collapsible into lowered position adjacent the surface of the platform when not in use and/or prior to the final positioning of a semi-trailer on the railway car for transport.
2. Description of the Prior Art
Over the road motor tractor trailer combinations have been widely used for hauling freight. The trailer or van component of a tractor trailer combination may be disconnected from the tractor and is self supporting for loading, unloading and/or storage or other stationary usage. These trailers or vans are commonly provided with a relatively large downwardly facing bearing plate with a depending kingpin at the center for connection and disconnection with a hitch assembly on the truck or tractor of the combination.
Piggyback operations have grown up utilizing these vans or trailers positioned on railroad cars or flat cars and secured in position thereon for transport over railroad right-of-ways to provide a more economical basis of transportation for goods. A wide variety of hitch mechanisms and supports therefore mounted on piggyback flat cars have been provided by companies such as Pullman Standard, ACF and Flexivan. U.S. Pat. Nos. 3,035,081; 3,127,142; 3,185,421; 3,289,987; 3,348,502; 3,358,945; 3,358,955; and 4,225,276 disclose various piggyback systems for semi-trailers including hitch assemblies, latch systems and support mechanisms for securing trailers in place on flat cars for transport.
Pullman Standard has developed models LP-1, 2, 3, and 4 of a pullup trailer hitch and an inspection and maintenance manual is provided for these hitches. A typical piggyback flat car with hitches thereon is illustrated on page 240 of the Car and Locomotive Encyclopedia.
One of the problems associated with many trailer on flat car hitches is the fact that extremely high loads are present on the latch mechanism which must be capable of restraining movement of a kingpin longitudinally of the semi-trailer. This has resulted in complicated jaw mechanisms such as screw operated jaws shown in U.S. Pat. No. 4,225,276 or a rotary latch mechanism shown in U.S. Pat. No. 3,358,955.